This invention relates to housing and mounting assemblies for electronic systems and devices and methods of packaging thereof and more particularly to the packaging and assemblies of electronics of systems operable in environments subject to accelerations several thousands times that of gravity.
Guidance electronics for gun-launched vehicles must endure some of the most demanding environments of all flight vehicle avionics. The set back forces, balloting and spin rates are typically far beyond those experienced by tactical and in many cases strategic missiles. The structural support for the guidance electronics is unsurprisingly challenging. The practice of the prior art in guided munitions typically employs a parasitically complicated structural support for the electronics packaging. In many instances, the structural supports are inadequate, leaving the circuits assemblies to rely upon potting material encapsulation and/ or structural foams in order to protect the circuitry from the gun-launched, high-g, environment.
Unfortunately, the potting material is difficult to apply and control in production. The coefficient of thermal expansion (CTE) mismatch, contributes to failures related to temperature cycling. Potted electronics assemblies and structural foams are problematic where rework or repair is required. In addition, the circuit card form factor of many guided munitions is driven by the orientation and location of the electronics packaging within the aerodynamic shell, often resulting irregular, or at least in nonrectangular, planforms that do not readily lend themselves to high volume, low cost production.
Electronic packaging considerations for gun-launched guided munitions must include the survivability of each circuit card assembly and its interconnection with the rest of the electronic assembly. For comparison, tactical missile circuit card assemblies and interconnects may be designed to withstand 30 g acceleration, whereas a gun-launched electronics assembly will typically be designed to withstand up to 20,000 g acceleration. A typical practice in the art of gun-launch survivability has circuit card assemblies made substantially rigid with metal or, as discussed above, fully encapsulated in potting materials and/or structural foam.
Adding to the complicating challenges, some components, such as a crystal oscillator, require a specific orientation with respect to the setback forces generated during a gun launch. Board level interconnects (e.g., wire bonds, gull wing leads, solder balls, and similar electrical connections), die attachment means (e.g., adhesive or solder) and component package styles (e.g., bare die, small outline surface mount packages and the like) must be tailored to accommodate the high setback forces.
Circuit card assembly costs are another important aspect of this art because gun-hardened electronics designs experience considerably higher production volumes as compared to relatively limited volumes of tactical missile electronics produced over the life cycle of the avionics in question.
A principal object of this invention is to provide circuit card technology that is capable of surviving a gun-launch environment (including setback, spin rate and balloting) such as that from a 155 mm canon by substantially isolating the electronic subsystems from nose and canard loading. That is, an object is to environmentally protect the electronic assembly by completely supporting single-sided circuit cards where the circuit cards are not structural elements and concurrently provide a relatively large area for heat dissipation. An additional object is to provide guided munitions electronic packaging and packages that are easier and less expensive to produce compared to the prior art. An additional object is to minimize the number of electrical interconnections (e.g., solder joints and mechanical connectors) and thereby reduce the number of failure points and streamline the manufacturing process. An additional object of the present invention is to minimize the use of potting materials, if any, and thereby obviate the need for structural foam. An additional object is to exploit the use of commercial off-the-shelf devices wherever practicable. An additional object of the present invention is to maximize the testability to efficiently support a streamlined manufacturing process. An additional object of the present invention is to isolate the electronic subsystems from aerodynamic and thermal battery heat loads.
The card rack and stabilizer structure of the several embodiments of the present invention comprise high strength titanium beta alloy, hot isostatic processing (HIP) eliminating voids and assuring uniform properties, structural support elements integrated into a monocoque structure, whereby the radial rib design provides structural rigidity and maximizes the circuit card assembly thermal heat transfer area.